Compressor control



a. s. AKKMAN COEPRESSOR CONTROL Filed Biay 26, 1956 4 Sheets-Sheet l iNVENTOR EURTON EL AIKMAN ATTORNEY N 1938- a. s. AIKMAN COMPRESSOR CONTROL Filed May 26, 1936 4 Sheets-Sheet 5 \w M Q A g mm as w% Q INVENTQR BURTON E. AIKMAN ATTORNEY 30 driving motor.

Patented Nov. 1, 1938 UNITED STATES PATENT OFFICE balsam oomrlmsson ooN'raoL Burton 8. Alirman, Wiikinaburg, Pm, assignorto' The Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Application May 26, 1936, Serial No. 81',862

'3 (oi. sac-4) This invention relates to a control system for a fluid compressor and for the compressor drivin means, and more particularly to a control system responsive to the pressure oi the fluid compressed 5 .by the compressor for loading and unloading the compressor and for also controlling the compressor driving means.

It is customary in many fluid compressor installations. to control the. compressor driving means in response to variations in the pressure of the fluid compressed by the compressor so as to eiTeot operationof the compressor when this pressure falls below a predetermined value and to continue operation of the compressor until the pressure of the fluid compressed by the compressor increases to a higher predetermined value.

In the control systems now in use it is customary, on an increase in the pressure of the fiuid compressed to the predetermined .value, to

actuate the means for controlling the compressor driving means, either before the compressor is unloaded, or simultaneously with operation of the compressor unloading means, with the result that this control of the driving means is eflected while the driving me'ans is under substantially its maximum load.

In many installations the driving means is an electric motor and the control system includes a switch which opens and closes the circuit to this driving motor is under maximum load the switch will be required to interrupts, heavy current and considerable arcing and burning of the switch contacts will result. If the circuit to the com- 5 pressor driving motor is not interrupted until after the compressor is unloaded, which results in a. substantial reduction in the load on the driving motor and a corresponding reduction in the current taken by the motor, the strength of the 40 circuit to be interrupted by thecontrol switch will be greatly reduced and the arcing and'burn- Aug of the switch contacts will be reduced to a minimum. v l

It is one object of this invention to provide a 5 compressor control system for controlling the operation 01 a compressor and of an'electric driving motor therefor, and which operates to unload the compressor and thereby reduce the load on the compressor driving motor before the circuit 50 to the driving motor is interrupted so that the strength 01 the circuit which must be interrupted If this switch isopened while the.

which is responsive to the pressure of the fluid compressed by the compressor and which regulates the pressure of the fluid compressed by the compressor without the use of toggle lever and spring combinations or without the use of valves operating against pressures higher than atmospheric pressure.

Another object of the invention is to provide a compressor control system of the type described and having means to adjustably vary the fluid 10 pressures which the system is adapted to maintain without aflecting in ,a substantial manner the forces available for actuating portions of the control mechanism A further object of the invention is toprovide 15 a compressor control system of the type described and which is adaptedfor use in connection with a compressor driven by either an electric motor or by an internal combustion engine. I

Another object of the invention is to provide a 29 compressor control system for use in controlling a compressor driven by an electric motor, the control system including a switch for controlling the circuit to the driving motor and having improved means to produce a blast of air across the 25 switch contacts when the contacts are opened in order to quickly extinguish the are which is formed between these contacts.

A further object 01 the invention is to provide an improvedcompressor control system. 30

Other objects of the invention and features of novelty will be apparent from the following description taken in connection with the accompanying drawings, in which M Fig. 1 is a diagrammatic view of a fluid compressor driven by an electric motor and equipped with one embodiment of the control system provided by this invention;

Fig. 2 is a diagrammatic view of a. fluid compressor driven by an internal combustion engine and equipped with another embodiment of the control system provided by this invention;

Fig. 3 is an enlarged fragmentary view, largely in section, of a portion of the apparatus employed inthe control system shown in Fig. 2 of the drawings;

Fig.4 is an enlarged sectional view of the control apparatusemployed in connection with the compressor shown in Fig. 1 of the drawings;

Fig. 5 is a sectional view taken substantially 5 along the line 5-5 of Fig. 4; I

Fig. 6 is a view similar to Fig. 4 and showing thecontrol apparatus in the position to unload the compressor and to interrupt the circuit to the compressor driving motor; as

. Fig. 7 is an enlarged sectional view of a modifled form of compressor control apparatus embodyin'g this invention;

Fig. 8 is an enlarged sectional view of the control apparatus employed in connection with the compressor shown in Fig. 2 of the drawings; and

Fig. 9 is, a sectional view taken substantially along the line 99 of Fig. 8.

Referring to Fig. 1 of the drawings there is illustrated therein a fluid compressor I, which may be of any suitable well known construction, and which compresses fluid into a reservoir 2 by way of a pipe 4. The compressor I is driven by means of an electric driving motor 6, while a control device, indicated generally by the reference numeral 8, is provided to control the loading and unloading of the compressor and to also 1cgnirol the supply of current to the driving mo- The construction of the control device 8 is best shown in Figs. 4, 5 and 6 of the drawings, and as therein illustrated comprises a hollow 'casing l0 having a passage extending therethrough in which is interposed air straining material, such as curled hair indicated at I2, which is confined betweenperforated plates I4 and I6. One end of the passage through the, casing I0 opens on a mounting face formed on the casing and adapted to be secured against .a similar mounting face formed on the compressor surrounding the intake passage I8 leading to the inlet valve of the compressor.

The other end of the passage through the casing I0 terminates in a substantially circular opening in the face of the casing I0 which is surrounded by an annular sealing gasket 20, which may be formed of any suitable material such as rubber. v

The control device 8 has associated therewith valve means adapted to control the flow of fluid to the passage through the casing I0, and this valve means comprises a valve disc 22 which is pivotally supported by-means of a pin 28 on an arm 24 of a member 28.

The member 28 is pivotally supported from a casing section by means of a pin 82 and is yieldingly urged in a counterclockwise direction, as viewed in Fig. 4 of the drawings, by means of a coil spring 84 which has one end connected to the pin 28 and has its other end connected to a threaded eye 86 which extends through an opening in the casing section 80 and has secured thereon a knurled nut 88.

The member 28 has an arm 40 formed integral therewith and this arm carries at the end thereof a roller 42 which is engaged by a member 44 which is pivotally secured by means of a pin 48 to a portion of the casing section 80.. The member 44 is yieldingly urged into engagement with the roller 42 by means of a spring 48 which has one end secured to a portion of the casing section 80 and has its other end secured to a threaded eye 50 which extends through an opening in the mensbzer 44 and has secured thereon a knurled nu The member 44 has a recess 84 formed in the I face thereof, and in one position of the arm 40 of the member 28 the roller 42 extends into the recess 54.

The member 28 has an arm 88 formed integral therewith and thirarm has a round portion 88 formed on the end thereofwhich extends into a hollow plunger 60 which is mounted in a bore in the casing section 80. The plunger 80 is provided with an enlarged head which engages one face of a diaphragm 82 which is subject on the other side to the pressure of the fluid in a chamber 64 which is connected by way of a pipe 66 with the reservoir 2 into which the compressor compresses fluid.

The rounded portion 58 of the arm 56 of the member 26 is engaged by means of a spring seat I0 which is slidably mounted in a bore in the plunger 80. A coil spring I2 extends between the springseat I0 and a latch piece I4 which is slidably mounted in a bore in the plunger '80, and

piston 80 also has formed thereon at a point substantially diametrically opposite the groove 84 a groove 86, and, as'will hereinafter more fully appear, the projection I8 on the latch piece I4. is

adapted at certain times to extend into this groove to hold the piston 80 in one of its positions.

The piston 80 has secured on the face thereof a movable contact 88 having spherical end portions which are adapted to engage stationary contacts 90 and 92. The movable contact 88 is ,secured to the piston 80 by means of a screw .94

and is insulated from the piston by means ofinsulating members 96 and 98.

The stationary contact 90 is connected by way of a wire 9| with one terminal of the driving motor 6, while the stationary contact 92 is connected by way of a wire 98 with one terminal of the source of current supply. The other terminal of the source of current supply and the other terminal of the driving motor are connected to ground.

The stationary contacts 90 and 92 are secured;

on a member I00 which is formed of suitable insulating material and is mounted in a recess in the member 90 so as to form a chamber I02- enclosing the stationary and movable contacts.

The stationary contacts 90 and 92 have restricted openings I04 and I08 extending therethrough and opening 'on the faces of the contacts which are adapted to be engaged by the movable contact 88.

The piston 80 has at one side thereof a II5 to aposition to press the movable contact 88 against the stationary contacts 90 and 92 and complete the circuit between these contacts.

The control device 8 is shown in Fig. 4 of the drawings in the position to complete the circuit to the compressor driving motor, to effect loading of the compressor, and with the pressure of the fluid compressed by the compressor below the value to whichthe control device is adapted to ,3%,248 respond to unload the compressor and to interrupt the circuit to the driving motor.

On -an increase in the pressure 'of the fluid compressed by the compressor I there will be a similarincrease in the pressure 'of the fluid in' the chamber 64 as this chamber communicates with the reservoir 2 by'way of the pipe 66. When the pressure of fluid in chamber 64 has been increased to a predetermined degree suflicient to overcome the opposing pressure of the spring 34 which acts through the arms 24 and 56 and the plunger 60 to'oppose movement of the diaphragm, said diaphragm will be moved upwardly, so as to cause the member 26 to be moved in a clockwise direction about the pin 32.

On this movement of theimember 26 the arm.

24 is moved and it will move the valvedisc 22 closer to the sealing gasket 20.

In addition, on this movement of the lever 26 the arm 40 thereof will be moved and the roller 42 will move across the face of the member 40 towards the depression 54. The face of the member 44 is arranged so as-to ofler substantially no opposition to movement of the roller towards the depression 54.

On this movementof the plunger the latch piece I4 will be moved towards the piston 80, and after a predetermined amount of movement of the plunger 60 upwardly the projecting portion 78 on the latch piece 14 will engage the face of the piston 00 so that on further upward movement of the plunger 60 the plunger will move and will compress of the plunger 00 the member 26 will be moved' an amount sufficient to move the valve disc- 22 very close to the sealing gasket 20 so as to substantially restrict the rate at which air may flow from the atmosphere to the passage through the casing section i0 leading to the inlet passage of the compressor. r

As the valve disc 22 approaches the sealing gasket 20, the flow of atmospheric fluid to the inlet passage of the compressor is substantially restricted, so that the atmospheric pressure acting on the outer face of the disc 22 against the partial vacuum created by the suction of the compressor at the opposite side of the disc by the movement of the disc toward its seat will cause the rapid movement of the disc to its closed position.

On movement of the valve disc 22 to the seated position the member 26 is moved in a clockwise alignment with the recess 54, whereupon the.

spring :38 causes the member 44 to move about the pin 66 so that the recessed portion 56 engages the roller 52.

On movement of the valve disc 22 to the seated position, because of the force exerted on the valve disc as a result of the partial vacuum'in the compressor inlet passage 'there will be a reduction in the force exerted by the'spring 30 on the plunger 00 and the plunger 00 will be moved upwardly by' the fluid under pressure in the chamber be acting on the diaphragm 62 into engagement with the shoulder I20 on the casing section 30, thereby increasing the amount ofcompression of the spring I2 and more, firmly pressing the latch piece "against the piston 30.

On a reduction in the pressure of the fluidin the compressor intake passage I8 there will be a similar reduction in the pressure of the fluid in the chamber I08 as this chamber communicates with the compressor intake-passage by way of the passage I l0. Fluid flows from chamber I 02 at one side of piston 00 through the restricted port 'I I4 in the piston to chamber I08, 5 but since the fluid pressure in chamber I08 is reduced at a greater rate than fluid can flow through said-port, the piston 80 will be moved to the right, against the resistance of the spring III by the higher atmospheric pressure in cham- 1 her I02. u

On this movement of the piston 00 the bridging contact 88 is moved awayirom the stationary contacts 90 and 92. When the bridging contact 08 is moved away from. the stationary contacts" 15 and 92 arcs may be formed between the stationary contacts and the bridging contact, but asthe compressor has already been unloaded before the bridging contact is moved away from the stationary contacts the load on the driving motor 01 the 20 compressor is reduced to a minimum, and the current required by the motor is also reduced to a minimum so that the size of the arcs which are formed ,on interruption of the circuit to the driving motor is at a minimum.- 0n movement of the piston 80 to the right, as viewed in Fig. 4 of the drawings, there will be an increase in the volume of the chamber I02 and a corresponding reduction in the pressure of the fluid in this chamber. As a result of the reduc-- tion in the pressure of the fluid in the chamber I02 from this cause, as well as from the flow of fluid therefrom through the passage II4 to the. chamber I08 and thence to the compressor intake-passage, the pressure of the fluid in the chamber I02 will be substantially below that of the atmosphere and air will flow through the passages I04 and Wm the chamber I02 and is discharged substantially in the zone of the arcs which form between the stationary contacts and the bridging contact 88 and serves to cool and extinguish these arcs.

As long as the compressor continues to operate there will be a,high degree of vacuum in the compressor' intake passage and fluid will continue to flow thereto from the chamber I02 throughthe passagelid, the chamber I08 and the passage 5 l0. As a result air will continue to flow through the passages I00 and I05 to the chamber I02 to extinguish the arcs formed on the interruption of the circuit to the compressor driving motor and to cool the switch contacts as long as the compressor continues to. operate.

I When the piston. 00'has moved substantially to the end of the bore in which it is located the projecting portion I0 of thelatch piece 14 is forced into the groove in the piston 80 by the spring 12 and extends beyond the shoulder at the end of the groove 80 so as to prevent return movement of the piston 80 by the spring H5.

The control device 8 is now substantially in the position in which it is shown in Fig. 6 of the drawings. As the bridging contact 08 has been moved away from the stationary contacts and 92 the circuit to the compressor driving motor is interrupted and this motor ceases to operate. The compressor, therefore, will not be driven and the partial vacuum in the compressor intake passage it will be gradually dissipated by the flow of air thereto from the atmosphere through the passages ltd-and I06 through the stationary'contacts 90 and 02, the chamber 802, the passage Ill through the piston 00, the chamber I00 and thence'by way of the passage H0. The piston 80 will be urged to the left, as viewed in Figs. 4 and 6 of the drawings, by the spring I I but its move-- ment will be prevented by the projecting portion 18 on the latch piece 14.

As the pressure in the compressor intake passage increases to atmospheric pressure the force exerted on the valve disc 22 and tending to maintain it in engagement with the sealing gasket 20 is reduced, but this valve is held in the seated position by the fluid under pressure in the chamber 64' acting through the diaphragm 62 and plunger 60, and by the spring 48 acting through the member 44 and pressing upon the roller 42 carried by the arm 40 of the member 26 on which the valve disc 22 is mounted. Because of the shape of the depression 54 in the'member 44 movement of the roller 42 out of the depression is prevented until the force tending tomove the roller in the opposite direction is reduced to a value substantially below that initially required to effect movement of the roller 42 into the depression 54.

When the pressure of fluid in the reservoir 2 and in chamber 64 is reduced sufliciently, the force of the spring 34 will act against the reduced pressure in chamber 64 and any resistance to movement offered by the spring 48, to move the member 26 in a counter-clockwise direction, so that the disc 22 is moved away from its seat to thereby open the compressor intake passage to the atmosphere.

On this movement of the member 26 the roller 42, which is carried by the arm of the member 26, moves out of the depression 54 in the member 44, and in moving out of the depression 54 the roller 42 moves the member 44 in a clockwise direction about the pin 46,' thereby increasing the tension'on the spring 48. Afterthe initial movement of the roller 42 out of the depression 54 it engages the flat face on the member 44 so that further movement of the roller 42 does not effect a further increase in the tension on the spring 48.

On movement of the member 26 by the spring 84 the round end 58 of the arm 56 engages the plunger 68 and moves the plunger downwardly,

as viewed in Figs. 4 and 6 of the drawings, and

and on this movement of the plunger 68 the pin 16 engages a shoulder on the latch piece 14 and retracts this latch piece so that the projecting portion 18 on the latch piece 14 is moved out of the groove 86 in the piston 80, thereby releasing the piston 88.

On the release of the latch piece 14 the piston 80 is moved by the spring H5 to the left, as

viewed in Figs. 4 and -6 of the drawings, thereby moving the bridging contact 88 into engagement with the stationary contacts 90 and 92, thus completing the circuit to the driving motor 6 for the compressor so that the motor is started andoperates the compressor to'compress fluid into the driving motor may be adjustably varied.

This is accomplished by turning the knurled nut 38 which varies the tension on the spring 34. If the tension on this spring is increased the pressure to which the fluid in the reservoir 2 and in the chamber 64 must build up before the valve disc 22 will be moved against the spring 34 to unload the compressor will be increased.

Similarly, if the tension on the spring 34 is. 7

- cult to the driving motor is not affected by this change in the adjustment of the spring 34 any change in the adjustment of the spring 34 to vary the pressure at which the control device operates to interrupt operation of the compressor will produce a similar change in the pressure at which the control device operates to initiate operation of the compressor. I The control device provided by this invention also incorporates means by which the difference in the pressure at which the operation of the compressor is interrupted and the pressure at which the operation of the compressor is initiated may be adjustably varied. This is accomplished by turning the knurled nut 52 and thereby varying the tension on the spring 48. If the tension on this spring is increased the force exerted by the spring and opposing movement of the roller '42 out of the depression '54 after movement of the roller into this depression will be increased, and hence the pressure of the fluid in the chamber 64 must decrease to a greater degree before the force exerted by this fluid on the diaphragm 62 and through the plunger 60 on the member 26 will be enough less than the force exerted on the member 26 by the spring member 34 that the member 26 will be actuated to move the roller 42 out of the depression 54 and to move the latch, piece 14 to release the piston 80.

Similarly, it the tension on the spring '48- is decreased, the force exerted by this spring and opposing movement of the roller 42 out of the depression 54 after movement of the roller into this depression will be decreased, and hence the pressureof the fluid in the chamber 64 must only decrease to a somewhat lesser degree before the force exerted by this fluid on the diaphragm 62 and through the plunger 60 on the member 26 will be enough less than the force exerted on the member 2'6 by the spring 34 sothat the member 26 will be actuated to move the roller 42 out of the depression 54 and to move the latch piece 14 to release the piston 80.

It will be seen that the control device provided by this invention incorporates means re-' sponsive to the pressure of the fluid compressed by the compressor for unloading the compressor and for interrupting the circuit to the driving motor of the compressor, and that it. operates so as to unloadthe compressor and reduce the load on the driving motor before the circuit to the driving motor is interrupted. with the result that the strength of the current to be interrupted is at a minimum.

It will be seen also that the control device provided by this invention incorporates means to create a blast of air between the contacts at the-time they are separated so as to cool and extinguish the arcs which are formed at this time, and that the means for creating this blast of air is responsive to operation of the compressor so that the air blast continues as long as the compressor continues to run.

It will be seen, in addition, that the control device provided by this invention is not dependent upon toggle lever and spring arrangements and does not employ valves operating against pressures above atmospheric pressure.

In addition it will be seen that the control device provided by this invention incorporates means to adjustably vary the pressure to which ing a chamber therein in which is positioned suitable airstrainingmaterial, such as curled hair indicated at I32, and which is confined by means '01 perforated plates I34 and I36.

The chamber I38 at one side of the air straining means I32 communicates with an opening in a mounting face on the body I30 which is adapted to be secured to a similar mounting face on a compressor so that the chamber I38 is in communication with'the intake passage of the compressor.

The chamber I40 on the other side of the air straining means I82 is open to one face of a diaphragm I42, which is subjecton the other side to the pressure of the fluid in a chamber I44, which is connected by way of a pipe I46 with the reservoir into which the compressor to be controlled compresses fluid.

One face of the diaphragm I42 is engaged by a plunger I43 which is mounted in the .chamber I40 and which carries a valve I50 which is adapted to engage a seat rib I52 .to control communication between-the chamber I40 and the atmosphere.

An end of the plunger I48 engages an arm I56 of a bell crank I56 which is pivotally supported on a pin I56. The arm I54 of the bell crank I56 is yieldingly urged in a counterclockwise direction, as viewed in Fig. 'I of the drawings, into engagement with a stop I65 by means of'a coil spring I60 which is secured to an eye I62 which extends through an opening in the arm I54,.and which has mounted on the end thereof a nut I60 by means of which the tension on the spring I60 may be adjustably varied.

The bell crank E56 is also provided with an arm I66 through which extends a plunger I66 which is slidably mounted in a bore in the casing section I30. A spring I10 is mounted on the plunger I66 and extends between a flange I12 on the plunger I66 and a face of the arm I66 of the bell crank I56.

The plunger I66 also has secured thereon a washer I14 which is held by means. of'a cotter pin I16 and which limits movement of the plunger I63 by the spring I10;

The spring H is under initial compmsion and holds the washer I14 in engagement with rounded projections I13 on the lower face of the arm I66 of the bell crank I66, and the'various parts oi the apparatus .arearranged and proportioned so that when the washer -I |4"is in engagement with the projection I13,a nd when the arm "I54 is in engagementwith the stop '"l65,- the end of the plunger I33 will notextendinto the bore in the casing section I30 in which is mounted a piston I60.

The piston I30, which is mounted in a bore in the casing section I30, is provided with a groove I62 into which extends a pin I84 to prevent rotation of the piston in this bore.

The piston I60 has formed on the opposite side from the groove I62 another groove I36 into which is adapted to extend, as will hereinafter more fully appear, the end of the plunger I68.

The piston I80 is yieldingly urged to the left, as viewed in Fig. 7 of the drawings, by means of a coil spring I86 which is mounted in a chamber I90, which is connected by way of a passage I92 to the chamber I38, and thereby to the compressor intake passage. Communication between the chamber I90 and the chamber I36 through the passage I92 is controlled by means of a valve I96.

The piston I00 has secured thereto, but insulated therefrom, a bridging contact I96 which- The contact I96 has a passage 2I0 extending therethrough and'opening on the face of the contact which is engaged by the bridging contact I96, while the contact 200 has a passage 2I2 ex tending therethrough and opening on the face of this contact which is engaged byv the bridging contact I96. The piston I30 has a restricted passage 2I4 extending therethrough and-communieating with the chamber I80 on the spring side of the piston and with the chamber 206.

This control device is shown in the drawings in the position to effect loading of the compressor, to complete the circuit to the compressordriving motor, and with the pressure of the fluid compressed by the compressor below the value to which the device is adjusted to respond to unload the compressor and to interrupt the circuit to thecompressor driving motor. The compressor, therefore, will be operated by the driving motor and will compress fluid under pressure into the reservoir associated with the compressor.

On an increase in the pressure of the fluid in the reservoir associated with the compressor there will be a similar increase in the pressure of the fluid in the chamber I44 on the face oi the diaphragm I42, and a correspondingincrease in the force exerted on the diaphragm I42 in opposition to the spring I60, whichoperates through the arm I54 of the bell crank I56 and the plunger I48.

As the pressure of the fluid in the chamber I44 increases the diaphragm I42 will be moved to the left, as viewed in Fig. 7 of the drawings, thereby moving the plunger I46, and its movement will be transmitted to the arm I54 of the bell crank plunger I63 it engages the face of the piston I33 so that on further upward movement of the arm 15 I66 of the bell crank I56 the spring I10 is compressed, and during this period the spring I10 opposes movement of the bell crank I56 by the fluid under pressure in the chamber I44.

When the pressure of the fluid compressed by the compressor is increased to a. predetermined value the force exerted by the fluid under pressure in the chamber I44 is sumcient to move the diaphragm I42 against the combined opposition of the springs I60 and I10 and the valve I50 will be moved adjacent the seat rib I52. As the compressor is being operatedat this time air is continuaily drawn into the chamber I40 past the seat rib I52, and when the valveI50 is moved adjacent to the seat rib I52 so as to substantially restrict the rate of flow of fluid past the seat rib I52 a relatively high' vacuum will be created in the chamber I 40.

On this reduction in the pressure of the fluid in the chamber I40 the effective pressure of the fluid in the chamber I 44 on the opposite side of the diaphragm I42 will be increased, and there will be a corresponding increase in the force exerted bythe fluid in the chamber I44 on the diaphragm I42 and tending to move the plunger I48 against the combined opposition of the springs I60 and I10.

As a result of this increase in the force exerted by the fluid under pressure in the chamber I44 the plunger I48 will be rapidly moved against the springs I60 and I10 and will move the valve I50 into engagement with the seat rib I52 so as to prevent the supply of fluid under pressure from the atmosphere to the chamber I40 and thence to the compressor intake passage.

As a result of this movement of the plunger I48 the bell crank I56 will be moved in a clockwise direction and the compression of the spring I10 will be increased, thereby pressing the plunger I68 more firmly against the face of the piston I80.

On the establishment of a relatively high degree of vacuum in the compressor intake passage fluid flows thereto from the chamber I90 on the spring side of the piston I80 through the passage I92, assuming that the valve I94 is in the open position, thereby reducing the pressure in the chamber I90. On a reduction in the pressure of the fluid in the chamber I90 fluid flows thereto from the chamber 208 through the'passage 2I4, thus reducing the pressure of fluid in the chamber 208. The rate of flow of fluid from the chamber 208 through the passage 2I4 is substantially less rapid than the rate of flow of fluid from the.

be moved by the fluid in the chamber 208 against the spring I88.

) A On this movement of the piston I80 the bridgspringyl88 the volume of the chamber 208 is in-' creased, thereby further reducing the pressure of the fluid in this chamber. As a result of the reduction in the pressure of the fluid in the chamber 208 air from the atmosphere flows through contact and the stationary contacts.

Fluid will continue to flow from the chamber 208 through the passage 2I4 to the chamber I90 on the'spring side of the piston I80, and therefrom through the passage I92 to the chamber I38 leading to the compressor intake passage, as long as the compressor continues to operate. As a result of the flow of fluid from the chamber 208 air will continue-to flow from the atmosphere through the passages 2 I0 and 2I2 so that the air blast which serves to extinguish the arcs formed on the interruption of the circuit to the driving motor and to cool the contacts continues to flow as long as the compressor continues to operate.

On movement'of the piston I80 against the spring I88 substantially to the end of the bore in which the piston I80 is mounted, the piston moves to aposition in which the groove I86 is in alignment with the end of the stem I68 so that the stem I68 is forced into the groove I86 by the spring I10. This serves to lock the piston I80 and to prevent its return by the spring I88 when the compressor ceases to operate and the pressure of the fluid in the compressor inlet passage is restored to atmospheric pressure by the flow of air thereto through the passage 2I 4 and the passage I92, or by other means.

On movement of the plunger I68 into the groove I86 the spring I10 expands somewhat, thereby reducing the force exerted by this spring on the arm I66 of the bell crank I56, and reducing the force tending to move the plunger I48 against the opposing force of the fluid under pressure in the chamber I44.

After the compressor ceases to be driven by the driving motor air from the atmosphere flows to the chamber 208 and therefrom by way of the passage 2I4, the chamber I90, and the passage I92 to the chamber I38 which communicates with the compressor intake passage. The pressure of v the fluidin the chamber I38, therefore, and also in the chamber I40, will be gradually restored to atmospheric pressure.

On an increase in the pressure of the fluid in the chamber I40 to atmospheric pressure, there is an increase in the force exerted by this fluid on the diaphragm I42 in opposition to the force exerted by the fluid in the chamber I44 and tending to maintain the control device in the condition to interrupt the circuit to the compressor driving motor.

The various parts of the control device are arranged and proportioned, however, so that the increase in force resulting from this increase in the pressure of the fluid in thechamber I40 and opposing the force exerted by the fluid in the chamber I44, is of lesser magnitude than the reduction in force opposing the force exerted by the fluid under pressure in the chamber I44 which occurs as a result of the expansion of the spring I10 whenthe plunger I68 is pressed into the groove. I 86 in the piston I80.

As a result of these changes in the various forces operative in the control device, there is an increase in the force effective to maintain the control-device in the condition to interrupt operation of the driving motor for the compressor.

On a reduction in the pressure of the fluid in the reservoir associated with the compressor controlled by this control device there will be a corresponding reduction in the pressure of the fluid in the chamber I44, and a similar reduction 70 ing contact I66 moves into engagement with the 1 I44 has reduced to a predetermined value the will result in the force exerted by this fluid on the diaphragm I42 and on the plunger I48 in opposition to the springs I68 and I18.

However, because of the reduction in the degree of compressionof the spring I18 'as-a result of movement of the plunger I68 into the groove I86 in the piston I88, the springs I18 and I6 8'will not exert enough force on the plunger I48 to move it against the opposing force of the fluid under pressure in the chamber I44 until a predetermined reduction in the pressure of the fluid in the chamber I44 has taken place.

On this predetermined reduction in the pressure of the fluid in the chamber I44 the springs I68 and I18 operating through the bell crank I56 will move the plunger I48 and the diaphragm I42 against the opposing force of the fluid under pressure in the chamber I44. I

On this movement of the plunger I46 the valve I58 is moved away from the seat rib I62, thereby again establishing communication from the atmosphere to the chamber I48, from which fluid flows to the compressor intake passage.

After acertain amount of movement of the arm I66 of the bell crank I56 the projection I18 engages the washer I14 so that on further movement of the bell crank I55 the plunger I68 is moved away from the piston I88.

When the spring I18 has expanded to a degree sumcient to press the projections I18 against the washer I14, this spring thereafter does not exert any force on the bell crank I56, and tending to move it against the opposing force of the fluid under pressure in the chamber I44 on the face of the diaphragm I42.

The bell crank I56, therefore, will be urged 3 stop I65 and the tension on the spring I68 is reduced.

Because of this gradual decrease in the force exerted by the spring I 68 the fluid in the chamber I44 must reduce to a somewhat lower, value before the bell crank I56 is moved to the position to move the 'plunger I68 to unlock the piston' I88 than was required to move the plunger I48 against the spring I68 to the position in which the valve restricted the flow of air past the seat rib I52 to a substantial extent. This is true as the parts of the control device are arranged so that the plunger I68 does not release thepiston I88 until the bell crank i66 is moved substantially into engagement with the stop I65, while the valve I58 does-not greatly restrict the flow oi fluid past the seat rib I52 until it has been moved towards the seat rib an amount sufficient to cause the arm I54 of the bell crank I56 to be moved a substantial distance away from the stop I65.

when the pressure of the fluid in the chamber bell crank I56 is moved into engagement with thereby releasing the piston, with'the result that the spring I68 moves the piston to the left, as

viewed in Fig. '1, in the bore in the casing I88.

On' this movement 01' the piston I68 the bridg stationary contacts I68 and 288,v thereby completing the circuit between these contacts and establishing a circuit to the driving motor or the compressor. a Y

on the completionoi the circuit to the cam- -pressor driving motor the motor operates to drive the compressor and causes it to compress fluid into the.reservoir"associated therewith. The compressor continues to operate'until the pressure of the fluid in this reservoir has increased to the value which is eflective to cause the control device to again operate as described in detail above to unload the compressor and to interrupt the circuit to the driving motor.

This control device incorporates 1 means to condition it to permit continuous operation of the compressor driving motor if desired, and to effect only unloading of the compressor on an increase to a predetermined value in the pressure of the, fluid compressed by the compressor and to maintain the compressor unloaded until the pressure of the fluid compressed by the compressor has decreased to a lower predetermined value. 20

If this method of operation is desired the valve I84 is turned to the seated position to cutofif communication between the chamber I38 and the chamber I88 on the spring side of the piston I88. With the control device conditioned for this method of operation the piston I68 is main- -tained bythe spring I68 in the position in which the contact I96 engages the stationary contacts I I98 and 288 to complete the circuit to the compressor driving motor.

The compressor will be driven by the driving motor, therefore, and, on an increase in the pressure of the fluid compressed by the compressor to a predetermined value the pressure of the fluid in the chamber I44 will exert ,a force.

on the diaphragm I42 sufllcient'to move the diaphragm I42 and the plunger I48 to the left, as

viewed in Fig. 7 of the drawings, thereby moving the bell crank I55.

, 0n initial movement of the bell crank I56 the v plunger I 8 is movedinto engagement with the piston I8 so that on further movement of the bell crank the spring I18 is compressed, while this movement of the bell crank I56 is opposed by the spring I68.

' 4'5 On a predetermined increase in the pressure of the fluid in the chamber I 44 the plunger I48 will be moved far enough against the springs I68 and I18 to move the valvei58 adjacent to the seat rib I52. As the compressor is being oper- 50 ated at this time air is drawn into the chamber I48 from the atmosphere and flows therefrom a to the compressor intake passage. When the flow of fluid to the chamber I48 from the atmos I I phere is restricted by movement of the valve I58 adjacent to the seat rib I 52 a partial vacuum will be created in the chamber I48.

This will reduce the pressure of the fluid on the face of the diaphragm I42 opposite frcmthe chamber I 44 and will increase the effective force 00 of the fluid under pressure in the chamber I54 acting on the diaphragm I42. The diaphragm I42 will thereupon be rapidlymoved to the left, as viewed in "Fig. 7, and will move the stem I68 to the left, thereby moving the valve I58 into engagement with the seat rib I52 to cut oil the flow of air from the atmosphere to the chamber I48 which communicates with the compressor inlet passage. 1

As communication between the chamber I38 "0 and the chamber I68 on the spring side or the piston. I88 through the passage I82 is cutoff by the valve I84 atthis time-the piston I. remains in the position to maintain the means 1 contact I86.in engagement with the. stationary 7 contacts I98 and 200 and thereby continue to cause the driving motor to drive the compressor.

I the driving motor, and as the valve I50 is maintained in engagement with the seat rib I52, a relatively high degree of vacuum will be present in the chamber I40 and in the other passages associated with the compressor intake passage, and this relatively high degree of vacuum operating upon the differential areas of the diaphragm I42 and the face of the valve I50 within the seat rib I52 increases the effective force of the fluid under pressure in the chamber- I44 operating on the diaphragm I42 and tending to maintain the plunger I48 in the position to unload the compressor. I

On a reduction in the'"pressure of the fluid inthe reservoir associated with the compressor controlled by this control device there will be a corresponding reduction in the pressure of the fluid in the chamber I44, and a similar reduction in the force exerted by the fluid in this chamber on the diaphragm I42 and tending to maintain the plunger I48 in the position to unload the compressor.

Because of the partial vacuum in the chamber I40 the pressure of the fluid in the chamber I44 on the face of the diaphragm I42 mustreduce to a somewhat lower value than is effective to move the plunger I48 to the position to unload the compressor before the springs I60 and I will be able to overcome the forces tending to maintain the plunger I48 in the position to unload the compressor.

However, when this reduction in the pressure of the fluid in the chamber I44 has taken place the springs I60 and I10 operating through the bell crank I56 move the plunger I48 against the opposing force of the fluid under pressure in the chamber I44 acting on the diaphragm I42, thereby moving the valve I50 away from the seat rib I52. I

On movement of the valve I50 away from the seat rib I52 air from the at nosphere flows past the seat rib I52 to the chamber I40 and increases the pressure of the fluid in this chamber. This increases the pressure on the face of the diaphragm I42 and decreases the effective force of the fluid under pressure in the chamber I44 on the opposite side of the diaphragm I42.

As a result, therefore, the springs I60 and H0 will thereupon rapidly move the plunger I48 to the right, as viewed in Fig. '7 of the drawings, until the bell crank I56 has been moved into engagement with the stop I65. v

The compressor is now unloaded and as it continues to be driven by the driving motor it will compress fluid under pressure into the reservoir associated therewith, and will continue to do so until the pressure of the fluid in this reservoir ,2

has increased to a value sufficient to cause the control device to again operate as described in detail above to unload the compressor.

This control device incorporates means by which the pressure to which the device is responsive to effectunloading of the compressor I60 the compressor will be unloaded in response to a somewhat lower pressure in the reservoir associated therewith.

In Figs. 2, 3, 8 and 9 of the drawings I have illustrated a, form of control device embodying this invention and adapted for use in connection with a compressor driven by an internal combustion engine.

As shown in Fig. 2 of the drawings there is av compressor 200, which may be of any suitable well known construction and is driven by means of an internal combustion engine 20I, which'may also be of any suitable well known construction;

The engine 20I is provided 'with an intake manifold 203 having a fuel supply device in the 7 form of a carburetor 205 associated therewith. The carburetor 205 includes a throttle valve 208, which controls the supply of fuel from the carburetor to the engine, and this throttle valve The compressor as shown in Fig. 2 of the' drawings has a control device indicated generally by the reference numeral 220 associated therewith, and operative in response to variations in the pressure of the-fluid compressed by the compressor to control the supply of fluid under pressure to and the withdrawal of fluid from the control device 2I6 and thereby control the position of the throttle valve 208 of the engine .The construction of the control device 220 is best shown in Figs. 8 and 9 of the drawings, and as shown in Fig. 8 of the drawings, the control device 220 comprises a hollow body 222 having a passage extending therethrough in which is interposed suitable air straining material, such as curled hair indicated at 224, which is confined between perforated plates, one of which is indicated at 226.

The passage through the body 222 communirounding the compressor intake passage 22 8.

The control device 220 includes, in addition,

a movable abutment in the form of 'a diaphragm 230 which .is subject on one side to the pressure of the fluid in a chamber 232 which communicates by way of a choke 234 and a pipe 236 with the reservoir 238 into which the compressor compresses fluid.

The diaphragm 230 has secured thereto a hollow stem 240 which is adapted to engage a stop 242 to limit movement of the diaphragm 230 and the stem 240 in one direction.

The stem 240 has an opening extending therethrough in which is mounted a valve 244 which is urged to the seated position by means of a "spring 246 mounted in a bore in. the stem 240 and extending between a shoulder on the stem 240 and a spring seat 248 which is secured on the valve 244.

The stem 240 has an annular recess formed therein and adapted to receive substantially round projections 250 carried by arms 252 which are pivotally supported on a pin 254 and which I have their free ends joined by means of a member 266. One end of a spring 258 is connected to the member 256 and the other end ofthis spring is connected 'to an eye 268 which extends through an opening in the body of the control device and has a knurled nut 262 secured on the end thereof. v

The control device 228 has associated there.- with a valve 266 having a head which is slidably mounted on the end of the stem 248, and having a tubular guide'portion 268 which is 'slldably mounted in a bore in the body of the control device. The head of the valve 266 carries a sealing gasket 218v which is adapted to engage a seat rib 212 to cut off communication between the atmosphere and a passage 214 leading to the compressor intake passage. The passage 214 is connected by way of a pipe 216 with a chamber 218 in the control device 2|6.

The valve 266 is yieldingly urged away from the seat rib 212 by means of a coil spring 268, while the tubular portion 268 of the valve 266 has a restricted opening 282 therethrough so as to establish communication with the chamber 284 within the tubular portion 268 and the passage .214.

The end of the valve 244 carried by the stem 248 is provided with. an enlarged head 286, which is adapted to be engaged by a portion of the head of the valve 266, as will hereinafter more fully appear.

This control device is shown in Fig. 8 of the drawings in the position to effect loading of the compressor, to condition the fuel supply device associated with the engine for driving the compressor to supply fuel to the engine at the maximum rate, and with the pressure of' the fluid compressed by the compressor below the pressure to which the control device is adapted to respond to unload-the compressor and to restrict the supply of fuel to the engine for driving the compressor.

On an increase in the pressure of the fluid in the reservoir 238 there will be a similar increase in the pressure of the fluid in the chamber 232 and a corresponding increase in the force exerted by this fluid on the diaphragm 238. Movement of the diaphragm 238 is opposed at this time by the spring 258 acting through the arms 252 and the projections 258 which engage the stem 248, and also by the spring 288 which opposes movement of the valve 266 to the closed position.

As the pressure of the fluid m the chamber 232 increases, however, the force exerted on the diaphragm 238 will increase, and when the pressure of the fluid in the chamber 232 has increased to a predetermined value the force ex-- erted on the diaphragm 238 will be sufficient to overcome the opposing forces of the springs 258 and 288. The diaphragm 238 and the stem 248 will thereupon be moved and the valve 266 will be moved towards the seat rib 212.

As the compressor is being operated at this time there is a rapid flow 'ofair from the atmosphere past the .seat rib 212 to' the passage 214 and thence to the intake passage 2280f the compressor. When the valve 266 is moved adjacent to the seat rib 212 so as to restrict the flow movement of the valve 266 ihto engagementwith' the seat rib 212.

The distance which the valve 266 has to be moved in moving to its seat after having been 286 on'the valve 244.

Because of the difference in the pressure of the fluid on opposite sides of the valve 266 a force will be exerted on this valve tending to move it to the seated position or to hold it in the seated. position after movement thereto against the opposing force of the spring 288. The force exerted by the spring 288, therefore, on the stem 248 to oppose movement of this stem by the fluid under pressure in the chamber 232 acting on the diaphragm 238 is accordingly reduced. Because of this reduction in the force exerted on the stem 248 in opposition to the fluid under pressure in the chamber 232, on movement of the valve 266 to the seated position the stem 248 will thereafter be moved very rapidly by the fluid under pressure in the chamber 232 and will press against the valve 266 and hold the sealing gasket 218 in engagement with the seat rib 212. i

The chamber 284 within the tubular. portion of the valve 266 communicates with the passage 214 by way of the restricted passage 282, and on a reduction in the pressure of fluid in the chamber 214 fluid flows thereto from the chamber 284 through therestricted passage 282. This results in a reduction in the pressure of the fluid in the chamber 284 and increases thearea of the valve 266 which is subject to the opposing pressures of the atmosphere and of the partial vacuum in the passages associated with the compressor intake passage and increases the force effective to hold the valve 266 in the seated position.

The various parts of the control device are proportioned so that when the valve 266 is moved to the seated position, and the fluid in the chamber 284 within the tubular po rtion 268 of the valve 266 is reduced substantially to the same pressure as the fluid in the-passage 214, the force exerted by the higher atmospheric pressure on the exposed face of the valve 266 and opposing the spring 288 exceeds by a substantial amount the force exerted on the valve 266 by the spring 288.

As the compressor continues to be operated by the driving motor a relatively high degree of vacuum will be .present in the compressor intake passage and also in the passages communicating therewith and air will be drawn through the pipe 216 from the chamber 218 of the control device 2l6. 1

On a reduction in the pressure of the fluid in the chamber 218 the higher atmospheric pressure on the opposite side of the piston 2 moves the piston 214 against the spring 218 and this movement of the piston 2M is transmitted through the link M2 to the lever 2l8 which operates the throttle valve 288.

On this movement of the piston 2 the throttle valve 288 is moved from the engine load position, inwhich positionfuel is permitted to be supplied to the engine at substantially the maximum rate, to the engine idling position, in which the supply of fuel to the engine is substantially restricted. This results in a reduction in the speed of the engine and of the compressor, but the compressor continues to be driven at a speed 'high enough to cause a relatively high degree of vacuum to be maintained in the compressor intake passages and in the associated passages. It will be seen, therefore, upon operation of the unloading means to effect unloading of the compressor the fuel supply to the engine for driving the compressor is restricted.

As the restriction in the supply of fuel to the engine does not take place until'the compressor has been unloaded there is no danger of the engine being stalled as a result of being overloaded. As the restriction in the supply of fuel to the engine takes place immediatelyupon operation of the unloading means there is no danger either that the engine will race or overspeed because of an excess supply of fuel thereto.

On a reduction in the pressure of the fluid in the reservoir 238 there will be a similar reduction in the pressure of the fluidin the chamber 232, and

a corresponding reduction in the force exerted.

by this fluid on the diaphragm 238.

tive to urge the stem 248 against the fluid in the chamber 232 at this time as the valve 288 is held in engagementwith the seat rib 212 by atmospheric pressure acting on the exposed face of the valve. The stem 248, therefore, is subject to the opposing pressures'of the fluid in the chamber 232 and of the spring 258, and the stemi248 will not be moved by the spring 258 until the pressure of the fluid .in the chamber 232 has reduced to a value such that the. force exerted by this fluid is less than the force exerted on the stern 248 by the spring 258. This pressure will be somewhat less than the pressure required to effect movement of the stem 248 to unload the compressor as this movement of the stem 248 is opposed by the spring, 288 in addition to the spring 258. v y

when the pressure of the fluid in the chamber 232 is reduced a predetermined low value such that the force exerted on the stem 248 by the spring 258 exceeds the opposing, force of the fluid under pressure acting on the diaphragm 238 and thereby on the stem 248, the stem 248 will be moved to the right, as viewed in Fig. 8 of the drawings,- by the spring 288 acting through the arms 282 and projections 258.

After-a predetermined amount of movement of the stem 248 the head 288 on the valve 244 seat the fluid under pressure present in the chamher 282 is permitted to escape therefrom at a rapid rate through the passage in-the stem 248 in which the valve 244 is loc'ated to the chamber 284 within the tubular portion 288 of the valve 288. the chamber 284 and reduces the force tending to hold the valve 288 in engagement with the seat rib 212, y

On movement of the valve 244 away from its seat fluid under pressure flows from the chamber 232 to the chamber 284 at a rapidrate, while fluid is permitted to'flow to the chamber 232 from the reservoir 238 by way of the pipe 238 and through the choke 284 onlyat a restricted rate.

'There will, therefore, be a rapid reduction in the pressure of the fluid in the chamber 232 as soon as the valve 244 is opened, and on this reduction in the pressure of'the fluid in the chamber 232 there will be a corresponding decrease in the force exerted on the diaphragm 288 and the spring 258 will thereupon rapidly move the stem 248 to the right until it engages the stop 242.

On the supply of fluid under pressure to the chamber 284 there is a reduction in the force valve 244 to the right, and on this movement of the valve 244 the head 288 presses against the head of the valve 288 and moves it away from the .fluid into the reservoir 238 until the pressure of the pressure of the fluid in the reservoir 238 and This increases the pressure of the fluid in to the position to condition the control device to tending to maintain the valve 288 against the seat'rib 212. The valve 288 may be moved away from the seat rib 212 at this time by the spring 288. If, however, the valve isnot moved .away

from the seat rib by the spring 288, on further 5 movement of the stem 248 to the right, as viewed in Fig. 8 of the drawings, the end of the stern 248 engages the spring. seat 248, so as to move the seat rib 212. on movement of the valve 288 away from th seat rib 212, air from the atmosphere flows past the seatn'ib 212 to the passage 214, thereby increasing the pressure of the fluid in the passage 214. On this increase in the pressure of the fluid in the passage 214 there is a reduction in' the forces tending to hold the valve 288.in th'e'seated position, and thevalve 288 will thereafter be moved very rapidly to the full openposition by the spring 288. a

On an increase in the pressure of the fluid in the cha ber 214 as a result of opening of the valve 28 fluid flows therefrom by way of the pipe 216 to the chamber 218 of the control de-' vice 216, and on an increase in the pressure of the fluid in this chamber the spring 2l8- moves the piston 2 to the right, as viewed in Fig. 3 of the drawings, and this movement of the piston 2 is transmitted through the link 2l2 to the arm H8 and moves this arm so as to move the throttle valve 288 from the engine idling position to the engine load-position.

The compressor is now in the loaded condition, while the engine is supplied with fuel at a rapid rate so as to drive the compressor and cause it to compress fluid into the reservoir 238. The com pressor will continue to operate and to compress the fluid in'this reservoir has increased to the value which is effective to cause the control device to again operate as described in detail above to unload the compressor and to restrict the supply of fuel to the engine for driving the compressor.

This-form of compressor control device incorporates means by which the pressure to which the device responds to unload the compressor and to reduce the supply of fuel to the engine may be adjustably varied if desired. This is accomplished by'turning the knurled nut 282 so as to vary the tension on the spring 258.

If the tension of the spring 288 is increased in .the chamber 232 must increase to a higher value before the force exerted on the diaphragm 238 exceeds the force exerted by the springs 288 and 288 and opposing movement of the stem 248 unload the compressor.

Similarly, if. the tension on the spring 288 is I decreased the force exerted by the fluid under pressure in the chamber 232 on the diaphragm 238 will exceed the opposing force oi the springs 288 and 288 on an increase in the pressure of the fluid in the chamber 232 to a somewhat lower value than before.

It will beseen that this form of compressor control device incorporates means responsive to the pressure of the fluid compressed by the compressor for effecting loading and unloading of the compressor, and that it includes, in addition, means responsive to operation ofthe unloading 2,18 6,248 means for controlling the means for driving the is not limited to these details of construction.

and' that numerous changes and modifications may be made without departing from the scope 10 of the following claims.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is: 1. In combination, a fluid compressor having I 15 an intake passage through which fluid is supplied to the compressor, valve means controlling the supply of, fluid to said intake passagadriving 'means for the compressor, meansresponsive to the pressure of the fluid in said intake passage 20 and controlling the driving means, said means comprising a control member movable between a cut-in position in which the driving means is conditioned to drive the compressor and a cutout position in which the driving means is con- 2. In combination, a fluid compressor having an intake passage through which fluid is sup- '5 plied to the compressor, valve means controlling the supply of fluid to said intake passage, driving means for the compressor, means responsive to the pressure of the fluid in said intake passage and controlling the driving means, said means comprising a control member movable between a cut-in position in which the driving means is conditioned to drive the compressor and a cut-out position in which the driving means is conditioned not to drive the compressor, an

abutment subject to and operated on a'prede- I termined increase in the pressure of the. fluid compressed by the compressor for operating the valve'means to cut off the supply of fluid to the intake passage, and latch means associated with said abutment. and operative on movement of the abutment to condition the valve means to cut oil the flow of fluid to the intake passage to permit the control member to move to the cutout position and on movement of the control member to the cut-out position to prevent movement thereof to the cut-in position.

3. In combination, a .fluid compressor having an intake passage, valve means controlling the flow of fluid to said intake passage, an electric motor for driving the compressor, apair of relatively movable contacts controlling the supply or current to the driving motor, said contactsbeing mounted in a chamber having communication with the compressor intake passage, means operated on a predetermined increase in the pressure of thefluid compressed by the compressor for closing said valve means and for thereafter eflecting separation --of said contacts and thereby interrupting the supply of current to the driving motor, and means operative on a reduction in the pressure of the fluid in said chamber to a pressure below atmosphere for creating a 'flow 01 air in the region between said contacts.

BURTON AIm/IAN. 

